15.1.7  Extracting samples from audio clips: channel_data

The channel_data command gets samples from an audio clip.

• channel_data takes one mandatory argument and up to two optional argument:
  • A, an audio clip.
  • Optionally options, which can be the following (the order is unimportant):
    • One of:
      • n, a postive integer (channel number).
      • matrix, the symbol.
    • One of:
      • range=[m,n] or range=m..n for nonnegative integers m and n.
      • range=a..b for floating point numbers a and b.
• channel_data(A ⟨,options⟩) returns data from the channels as a sequence of lists. The returned sample values are all within the interval [−1.0,1.0], i.e. the amplitude of the returned signal is relative. The maximum possible amplitude is represented by the value 1.0.
  • With no options, data from all channels are returned as a sequence of lists.
  • With the option n (the channel number) or if there is only one channel, only the data from this channel is returned in a single list.
  • With the option matrix, the lists representing the channel data are returned as the rows of a matrix.
  • With the option range=[m,n] or range=m..n, with m and n integers, only the samples from n-th to m-th (inclusive) are extracted.
  • With the option range=a..b, with floating point numbers a and b, then a and b are bounds in seconds.

Example.
Assuming that the directory sounds contains example.wav, a wav file with three seconds of stereo sound:
Input:

Output:
A list L resp. R containing the data between 1.2 and 1.5 seconds in the left resp. right channel of the original file.